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Wireless Power

Posted by: Sigurd - Sun Jan 21, 2007 3:59 pm
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Wireless Power 
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Post Wireless Power   Posted on: Sun Jan 21, 2007 3:59 pm
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The concept of wireless power is not a new one, but it is just now beginning to break out into the consumer world with real products that are (or almost are) actually in production. At last week's CES in Las Vegas, two companies—eCoupled and Powercast—introduced their "wireless" power systems to the awe of many spectators, in hopes of making our experiences with the fabled Cord Gnome a thing of the past.


http://arstechnica.com/news.ars/post/20070117-8639.html


Earlier on BBC & arstechnica.com:
http://news.bbc.co.uk/2/hi/technology/6129460.stm
http://arstechnica.com/news.ars/post/20061115-8229.html

Quote:
researchers have outlined a relatively simple system that could deliver power to devices such as laptop computers or MP3 players without wires.

The concept exploits century-old physics and could work over distances of many metres, the researchers said.



While inside a spaceship they might prefer to have a more reliable technique, like using shielded cables for magnetic interference etc.. For scientific experiments, or other techniques this creates a lot of new posibilities. We'll be able to have objects using energy with it being "always" closed from all sides. Without a physical link or a need to refuel it. One of the locations where it may become useful is in hazardous locations where we use pressurised air and other techniques today.

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Post    Posted on: Mon Jan 22, 2007 9:11 am
That's induction as far is i know. That's 'wireless' in a very literal sense and is not really being used over great distances. I'll bet the real wirelss energytransmitters will be those microwaves.


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Post    Posted on: Mon Jan 22, 2007 2:00 pm
It works for a few metres, so it's perfect for a normal home, kinda same as for those linksys wireless stations only this time for power.

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Post    Posted on: Mon Jan 22, 2007 10:38 pm
Spraying rf power around a house would be exremely bad news, besides upsetting most household electronic appliances it would slowly cook anyone sitting in it. Microwave ovens work at a frequency of 2.45GHz but other frequencies will perform the same function less efficiently.

Besides the heating effects some frequencies can effect behaviour and cause anxiety or cause resonance in body cavities. Anyone sitting in these rf fields will probably excede the recommended exposure limits for rf. Anyone interested in what those limits are (in the UK at least) should look at the nrpb (National Radiological Protection Board) website here;

http://www.hpa.org.uk/radiation/

You would probably need quite a large field density throughout a house to be able to power anything requiring more than a couple of watts or have localised hotspots. Generating a uniform field in someone's lounge would be virtually impossible due to the sources of reflection and absorbtion. Someone sitting in different positions within the room would cause the field to deform in different directions.

The losses of such a system would be horrendous, with maybe only a couple of percent of the power being transmitted being converted back to usable power.

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Post    Posted on: Tue Jan 23, 2007 1:59 pm
While the press does not (of course) go into technical detail on how this would work, it is clearly not broadcast power. Here is a quote from http://arstechnica.com/news.ars/post/20061115-8229.html
Quote:
Other wireless power systems include Nikola Tesla's long-range wireless energy experiment, the Wardenclyffe Tower (which ended when he ran out of funding); directional energy transfer such as lasers; and induction-based energy transfer systems such as the charger for electric toothbrushes. MIT's team hopes to improve upon these existing systems with their own solution, a type of longer-range induction, based on the resonance of an electromagnetic field. Outside of smaller applications, such as charging your toothbrush, this is something typically used in radio antennas. However, a radio antenna is inefficient for transferring energy because it broadcasts radio waves in all directions regardless of other devices—a waste of energy if used for powering devices wirelessly.

To remedy this, the researchers designed an emitter to make use of long-lived resonances with "non-radiative" objects. This keeps the energy close to the antenna until another object with a similar resonance comes within range—no broadcasting into space is necessary. The two resonating objects can sync their frequencies easily, which would then cause energy to "tunnel from one object to another," Professor Soljacic told the BBC. When not transferring energy to another device, "most" unused energy simply gets reabsorbed into the emitter.



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Post    Posted on: Tue Jan 23, 2007 6:41 pm
Not quite sure how this is supposed to work, if one assumes that some form of inductive loop is used in the resonant circuit to pick up the resonances from the emitters then how are the two circuits going to couple with each other without one radiating to the other?

Somethings to bare in mind:

Magnetic fields decay at a rate of 18dB per Octave or in simple terms a field of 1A/m at a separation distance between the transmitter and receiving circuits of 1m would drop to 0.125A/m at a distance of 2m and 0.015625A/m at 4m. As you can see you dont need to move very far away before there is very little left to detect.

Electric fields decay at a lower rate 6dB per Octave. But both will decay at even faster rates due to near field effects.

The Near/Far field boundary is normally quoted as being Wavelength/2PI.

For example at a frequency of 50MHz this boundary would be at approximately 1m. I must admit that a lot of research has gone on to determine what is going on in the extreme near field and there is still a great amount of uncertainty with regard to modelling it so it is possible that this group has found something that allows this device to work, unlikely but possible.

As an aside the article says that radio antennas broadcast in all directions, while this is true for something like a rod antenna it is not correct for Horn and dish antennas or LogPeriodic antennas so I dont see why this is said to be a problem. The field strength would decay at the same rate irrespective of the type of antenna that propogated it.

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Post    Posted on: Fri Feb 02, 2007 6:57 pm
JPL's Neville Marzwell wants to power devices directly from SPS systems.


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Post    Posted on: Fri Feb 02, 2007 10:04 pm
I can't imagine direct SPS power for many things outside of specific rectenna arrays. Possibly certain major highways, maybe a directed beam for trains, airplanes and ships but I doubt it would be publicly accepted for much else. Even those could be an uphill battle. I just finished Ben Bova's 'Powersat' and I can all to easily imagine flocks of environuts protesting any SPS system. :?


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